Front contact solar cell with formed emitter

Abstract

A bipolar solar cell includes a backside junction formed by an N-type silicon substrate and a P-type polysilicon emitter formed on the backside of the solar cell. An antireflection layer may be formed on a textured front surface of the silicon substrate. A negative polarity metal contact on the front side of the solar cell makes an electrical connection to the substrate, while a positive polarity metal contact on the backside of the solar cell makes an electrical connection to the polysilicon emitter. An external electrical circuit may be connected to the negative and positive metal contacts to be powered by the solar cell. The positive polarity metal contact may form an infrared reflecting layer with an underlying dielectric layer for increased solar radiation collection.

1. A solar cell having a front side facing the sun to collect solar radiation during normal operation and a backside opposite the front side, the solar cell comprising:
 an N-type silicon substrate; 
 a textured surface on the N-type silicon substrate on the front side of the solar cell; 
 an antireflective layer over the textured surface of the N-type silicon substrate; 
 a P-type polysilicon emitter formed over the N-type silicon substrate and forming a backside junction with the N-type silicon substrate; 
 an oxide layer formed between the P-type polysilicon emitter and the N-type silicon substrate; 
 a negative polarity metal contact making an electrical connection to the N-type silicon substrate from the front side of the solar cell; and 
 a positive polarity metal contact making an electrical connection to the P-type polysilicon emitter from the backside of the solar cell. 
 
     
     
       2. The solar cell of  claim 1  wherein the antireflective layer comprises a layer of silicon nitride. 
     
     
       3. The solar cell of  claim 1  further comprising a dielectric layer over the P-type polysilicon emitter. 
     
     
       4. The solar cell of  claim 3  wherein the dielectric layer comprises silicon dioxide. 
     
     
       5. The solar cell of  claim 3  further comprising a trench cutting through the dielectric layer and the P-type polysilicon emitter and into a portion of the N-type silicon substrate on the backside of the solar cell. 
     
     
       6. The solar cell of  claim 1  wherein the positive polarity metal contact comprises a metal forming an infrared reflecting layer with a dielectric layer. 
     
     
       7. The solar cell of  claim 1  wherein the positive polarity metal contact comprises silver forming an infrared reflecting layer with a dielectric layer comprising silicon dioxide. 
     
     
       8. The solar cell of  claim 1  wherein the negative polarity metal contact comprises a metal formed in a contact hole to the N-type silicon substrate. 
     
     
       9. A solar cell having a front side facing the sun to collect solar radiation during normal operation and a backside opposite the front side, the solar cell comprising:
 a substrate having a textured front surface; 
 an emitter layer formed over a back surface of the substrate, the emitter layer forming a backside junction with the substrate; 
 an oxide layer formed between the back surface of the substrate and the emitter layer; 
 a first metal contact making an electrical connection to the substrate on the front side of the solar cell; and 
 a second metal contact making an electrical connection to the emitter layer on the backside of the solar cell, the first metal contact and the second metal contact being configured to allow an external electrical circuit to be powered by the solar cell. 
 
     
     
       10. The solar cell of  claim 9  further comprising an antireflective layer over the textured front surface of the substrate. 
     
     
       11. The solar cell of  claim 9  wherein the substrate comprises an N-type silicon substrate and the emitter layer comprises a P-type doped polysilicon. 
     
     
       12. The solar cell of  claim 9  wherein the second metal contact comprises silver formed over a layer of silicon dioxide.